Gas-Phase Alloying and Sintering Kinetics of 3D Printed Ni Scaffolds

制造具有越来越复杂的几何形状的金属零件是几个行业感兴趣的问题。特别是，金属支架由于其低密度和高比表面积，在从电池到生物医学植入物的各种应用中都是很好的候选材料。然而，许多技术上重要的合金很难用传统的制造方法在脚手架几何形状中制造，即使是新的方法，如添加制造(通常称为3D打印)，也面临着巨大的挑战。一种通过两步法制造这些金属支架的新工艺已经形成了理论，这将使不同的材料能够从相同的前体印刷金属部件中生产出来。该奖项支持研究，以了解控制这一新过程的动力学和热力学的基本机制。由于金属脚手架结构在工程上的广泛应用，这项研究成果将促进包括能源、汽车和生物医药行业在内的许多制造行业的技术创新。通过招募和推广活动，STEM中传统上代表性不足的群体将参与这项研究工作，这将在早期吸引学生，并有助于使工程职业管道多样化。虽然能够制造具有高几何复杂性的近净形状金属零件的能力使粉末床添加剂制造技术具有吸引力，但许多工程相关合金由于烧结差、内部孔洞和开裂而难以制造出高质量的材料。一种替代方法是通过使用基于颗粒的油墨印刷来分离印刷和合金化，以从已知印刷成功的纯金属或简单合金创建所需的几何形状，然后在单独的步骤中使用沉积过程和均质化来进一步合金化部件以达到目标组合物。这种方法非常适合创建金属支架，利用开放的孔隙率和较小的扩散距离。该项目的总体目标是使用常规金相学和原位X射线断层扫描显微镜相结合的方法来研究此类支架的基本烧结和合金化动力学。系统地研究了晶相和气孔随几何形状、成分、粉末和支柱尺寸、热处理时间和温度的变化，并对其力学行为进行了计算预测和实验确定。

The fabrication of metal parts with increasingly complex geometries is of interest to several industries. In particular, metal scaffolds are good candidates for a variety of applications from batteries to biomedical implants, due to their low density and high surface area. However, many technologically important alloys are difficult to fabricate in scaffold geometries using traditional manufacturing, and even newer approaches such as additive manufacturing (often known as 3D printing), have significant challenges. A new process has been theorized for making these metal scaffolds through a two-step approach, which will enable an assortment of different materials to be produced from the same precursor printed metal part. This award supports research to understand the fundamental mechanisms of kinetics and thermodynamics that control this new process. Because of the wide range of engineering applications for metal scaffold structures, results from this research will promote technological innovations in a number of manufacturing sectors including energy, automotive and biomedical industries. Through recruiting and outreach activities, traditionally underrepresented groups in STEM will be involved in this research effort, which will engage students at an early age and help diversify the engineering career pipeline.While the ability to create near-net-shape metallic parts with high geometric complexity has made powder-bed additive manufacturing techniques attractive, many engineering relevant alloys are difficult to fabricate with high quality due to poor sintering, internal porosity, and cracking. One alternative approach is to decouple the printing and alloying by using particle-based ink printing to create the desired geometry from a pure metal or simple alloy that is known to print successfully, and then further alloy the part in a separate step using a deposition process and homogenization to reach the target composition. This approach is ideal for creating metallic scaffolds, taking advantage of the open porosity and small diffusion distances. The overall aim of this project is to study the fundamental sintering and alloying kinetics of such scaffolds using a combination of conventional metallography and in situ X-ray tomographic microscopy. The phase and pore evolution will be systematically studied as a function of geometry, composition, powder and strut size, and anneal time and temperature and the mechanical behavior will be computationally predicted and experimentally determined.